pulsar planets

Against all expectations, the first confirmed planetary system beyond our
own was found, in 1991, in orbit around a pulsar.
The object in question is a millisecond
pulsar known as PSR 1257+12. The discoveries
of several other planets around millisecond pulsars, made using the pulsar
timing method, have since been announced, though in most cases these are
awaiting confirmation. The nature and origin of these strange worlds is
a matter of debate.1, 2, 3 One possibility is that the pulsar
planets formed in the normal way (see planetary
systems, formation of) before their host star exploded as a supernova.
However, it is hard to see how this could be so. The problem is not that
the supernova would destroy any nearby planets (though it would certainly
incinerate any surface life), but that it would effectively loosen the gravitational
glue holding the planetary system together. A planet orbiting a star that
suddenly lost a large fraction of its mass would fly off into space. The
alternative, and more likely scenario, is that pulsar planets formed after
the pulsar came into existence. Millisecond pulsars are believed to spin
so fast because they have acquired material from a companion star. Planets
could condense from some of this material as it entered an accretion
disk in orbit around the pulsar. However they were made, these strange
and unexpected worlds are of little direct biological interest. The main
sequence lifespan of massive stars which are the precursors of pulsars
is probably too short to allow any kind of life to develop, even given the
availability of suitable planets nearby. On the other hand, planets which
formed around a pulsar would be permanently strafed by high-energy radiation,
including X-rays and gamma
rays, leaving them barren and inhospitable.

The table below shows those pulsar planets confirmed or suspected as of
January 2001.4